This application claims the benefit of a Japanese Patent Application No.2001-022415 filed Jan. 30, 2001, in the Japanese Patent Office, the disclosure of which is hereby incorporated by reference.
1. Field of the Invention
The present invention generally relates to magnetic recording and/or reproducing apparatuses, and more particularly to a magnetic recording and/or reproducing apparatus which records an arbitrary recording sequence on a magnetic recording medium and/or reproduces the arbitrary recording sequence from the magnetic recording medium.
2. Description of the Related Art
FIG. 1 is a system block diagram showing a general structure of an example of a conventional magnetic recording and/or reproducing apparatus. In FIG. 1, a recording system of the magnetic recording and/or reproducing apparatus includes an encoder 1, and a recording and/or reproducing section 2 which includes a magnetic head and a magnetic recording medium. A reproducing system of the magnetic recording and/or reproducing apparatus includes the recording and/or reproducing section 2, a lowpass filter (LPF) 3, a finite impulse response (FIR) filter 4, a Viterbi detector 5, a post processor 6, and a decoder 7.
At the time of the recording, the encoder 1 encodes a recording sequence into a code sequence which is added with a parity bit, and the recording and/or reproducing section 2 records the code sequence on the magnetic recording medium by the magnetic head. On the other hand, at the time of the reproduction, the recording and/or reproducing section 2 reproduces the code sequence from the magnetic recording medium by the magnetic head, and supplies the reproduced code sequence to the Viterbi detector 5 via the LPF 3 and the FIR filter 4. The Viterbi detector 5 converts an equalized waveform which is obtained by the equalization by the FIR filter 4 into a maximum likelihood sequence by a metric calculation based on an equalization target (ideal value). The post processor 6 carries out an error detection and an error correction using the parity bit, with respect to the maximum likelihood sequence which is supplied from the Viterbi detector 5. The error correction is made by comparing a sequence which is obtained by convolution of the maximum likelihood sequence and the equalization target, and the actual equalization target which is obtained from the FIR filter 4. The decoder 7 decodes the maximum likelihood sequence which has been subjected to the error detection and the error correction, so as to reproduce the original recording sequence.
FIG. 2 is a diagram showing the actual equalized waveform (average value) which is obtained from the FIR filter 4 and the equalization target (ideal value). In FIG. 2, the ordinate indicates a signal amplitude in arbitrary units, and the abscissa indicates a phase in arbitrary units. Further, symbols “x” indicate the actual equalized waveform, and symbols “o” indicate the equalization target.
In the conventional magnetic recording and/or reproducing apparatus, the metric calculation in the Viterbi detector 5 is made based on the equalization target, and an equalization error, that is, an error between the equalization target and the actual equalized waveform is not taken into consideration. For this reason, as may be seen from FIG. 2, there were problems in that it is impossible to cope with an error in the FIR filter 4 which becomes notable as the recording density on the magnetic recording medium becomes larger, or to cope with an error which is generated as the non-linear distortion becomes larger.
In addition, the error correction in the post processor 6 is also made based on the equalization target. For this reason, there was a problem in that a difference between the corrected waveform and the actual equalized waveform becomes large.
Accordingly, in the conventional magnetic recording and/or reproducing apparatus, it is difficult to carry out the detection of the maximum likelihood sequence and the error correction with a high accuracy.
Furthermore, in the conventional magnetic recording and/or reproducing apparatus, there is a limit to carrying out a recording compensation in the recording system with respect to the non-linear distortion, and it is becoming increasingly difficult to cope with the increase of the recording density on the magnetic recording medium.